Chimeric Fc-gamma Receptor and Method for Determination of ADCC Activity by Using the Receptor

ABSTRACT

An objective of the present invention is to provide chimeric receptors containing a mouse Fcγ receptor extracellular domain and a human Fcγ receptor transmembrane domain, or chimeric receptors containing a mouse Fcγ receptor extracellular domain and a human γ chain transmembrane domain. Another objective of the present invention is to provide methods for measuring the ADCC activity of mouse antibodies and methods of screening for mouse antibodies having ADCC activity, using the chimeric receptors. 
     To accomplish the above-mentioned objectives, the present inventors produced chimeric molecules by fusing the extracellular domain of mouse FcγR3 or mouse FcγR4 with the transmembrane domain/intracellular domain of human γ chain or human FcγR3, and expressed the chimeric molecules in human NK92 cells. It was revealed that the ADCC activity can be induced by the chimeric receptors produced by any combination of the domains, and that the ADCC activity of mouse antibodies can be measured using the chimeric receptors of the present invention.

TECHNICAL FIELD

The present invention relates to chimeric Fcγ receptors of a human Fcγ receptor or the human γ chain with a mouse Fcγ receptor.

BACKGROUND ART

When developing antibody pharmaceuticals with a drug action mechanism based on antibody-dependent cell-mediated cytotoxicity (ADCC), it is important to select clones with high ADCC activity. ADCC activity is evaluated using cells expressing an antigen of interest (target cells) and effector cells that kill those target cells. Effector cells recognize the Fc region of antibodies bound to the target cells via the Fcγ receptor (FcγR). Signals transmitted from FcγR causes the effector cells to kill the target cells. FcγR binds to a molecule called the γ chain through its transmembrane domain, and transmits ADCC signals via this γ chain (Non-patent Documents 1 to 3). Mouse FcγR3 and FcγR4, and human FcγR3 are known as FcγR4 that induce ADCC. Amino acid sequence comparisons of the transmembrane domains of human and mouse FcγR4 show that five out of the 21 amino acids are different between human FcγR3 and mouse FcγR3, and seven out of the 21 amino acids are different between human FcγR3 and mouse FcγR4. Human γ chain and mouse γ chain comparisons show that one out of the 21 amino acids is different between the sequences in the transmembrane domains (Non-patent Document 4).

When measuring the ADCC activity of human antibodies, human NK cells are used as effector cells. Human NK cells can be purified from human peripheral blood mononuclear cells (PBMC) using the NK Cell Isolation Kit II (Miltenyi Biotec K.K.). Alternatively, PBMC can be used directly as effector cells. PBMC can be purchased (from Cambrex Corporation), or can be prepared from fresh peripheral blood collected from volunteers. However, when such cells are used as effector cells, the drawbacks include lot-to-lot differences and laborious preparation.

To avoid such drawbacks, systems that use human NK cell lines as effector cells have been developed for measuring the ADCC activity of human antibodies. The NK92 human NK cell line (ATCC) does not express human FcγR, but expresses the human γ chain (Non-patent Document 5). Therefore, ADCC activity can be induced by forcedly-expressing human FcγR3 in the NK92 human NK cell line (Non-patent Documents 6 and 7). This greatly reduced preparation labor and enabled accurate measurements having small lot-to-lot differences. Furthermore, it has been reported that chimeric molecules produced by fusing the extracellular domain of human FcγR3 and the transmembrane domain and intracellular domain of human γ chain induce ADCC activity related to human antibodies (Non-patent Document 8).

On the other hand, when measuring the ADCC activity of mouse antibodies, mouse spleen cells are used as effector cells (Non-patent Documents 9 and 10). To prepare mouse spleen cells, it is necessary to remove the spleen from mice, hemolyze erythrocytes, and activate NK cells with interleukin 2. However, since spleen cells prepared in this manner have high natural killer activity to kill target cells in an antibody-independent manner, the ADCC activity may not be measurable depending on the type of target cells. Furthermore, preparation of the effector cells requires effort.

Systems for measuring the ADCC activity of human antibodies using human NK cell lines have been developed. However, since the use of mouse NK cell lines is generally unknown, a system for conveniently measuring the ADCC activity of mouse antibodies using an NK cell line has not been established. Furthermore, since there are sequence differences between Fcγ receptors and γ chains between human and mouse, even if mouse FcγR is expressed as it is in human NK92 cells, mouse FcγR will not be able to bind to the human γ chain with similar strength as human FcγR.

Therefore, to measure the ADCC activity of mouse antibodies, it was necessary to use a method that requires much effort such as the method of preparing mouse spleen cells as described above, or the method of preparing a chimeric antibody in which the antibody Fc regions have been replaced with those of a human antibody.

Prior art literature information relating to the present invention is shown below.

-   [Non-patent Document 1] Blood 2003, 101, 4479. -   [Non-patent Document 2] J. Immunol. 1991, 146, 1571 -   [Non-patent Document 3] Immunol. Lett. 2004, 92, 199 -   [Non-patent Document 4] J. Biol. Chem. 2006, 281, 17108 -   [Non-patent Document 5] Leukemia Res. 2003, 27, 935 -   [Non-patent Document 6] 97th AACR annual meeting 2006, abstract     number 635 -   [Non-patent Document 7] J. Biol. Chem. 2004, 279, 53907 -   [Non-patent Document 8] Blood 2006, 107, 4669 -   [Non-patent Document 9] Oncol. Rep. 2006, 15, 361 -   [Non-patent Document 10] Cell. Immunol. 1988, 115, 257

DISCLOSURE OF THE INVENTION [Problems to be Solved by the Invention]

An objective of the present invention is to provide chimeric receptors comprising a mouse Fcγ receptor extracellular domain and a human Fcγ receptor transmembrane domain, and chimeric receptors comprising a mouse Fcγ receptor extracellular domain and a human γ chain transmembrane domain. Another objective of the present invention is to provide methods for measuring the ADCC activity of mouse antibodies using the chimeric receptors. A further objective of the present invention is to provide methods of screening for mouse antibodies having ADCC activity using the chimeric receptors.

[Means for Solving the Problems]

To achieve the above-mentioned objectives, the present inventors produced chimeric molecules by fusing the extracellular domain of mouse FcγR3 or mouse FcγR4 with the transmembrane domain and intracellular domain of human γ chain or human FcγR3, and expressed the chimeric molecules in human NK92 cells. The present inventors found that any one of the combinations of mouse FcγR3 and human γ chain, mouse FcγR3 and human FcγR3, mouse FcγR4 and human γ chain, and mouse FcγR4 and human FcγR3 can induce the ADCC activity. Thus, the present inventors discovered that the ADCC activity of mouse antibodies can be measured by using a chimeric receptor produced from a mouse Fcγ receptor and a human Fcγ receptor, or a chimeric receptor produced from a mouse Fcγ receptor and the human γ chain. Furthermore, the present inventors discovered that mouse antibodies having ADCC activity can be screened for by using a chimeric receptor produced from a mouse Fcγ receptor and a human Fcγ receptor, or produced from a mouse Fcγ receptor and the human γ chain.

Specifically, the present application provides the following:

-   [1] a chimeric protein comprising a mouse Fcγ receptor extracellular     domain and a human γ chain transmembrane domain;

[2] the chimeric protein of [1], wherein the chimeric protein further comprises a human γ chain intracellular domain;

[3] a chimeric protein comprising a mouse Fcγ receptor extracellular domain and a human Fcγ receptor transmembrane domain;

[4] the chimeric protein of [3], wherein the chimeric protein further comprises a human Fcγ receptor intracellular domain;

-   [5] the chimeric protein of [3] or [4], wherein the human Fcγ     receptor is human Fcγreceptor 3; -   [6] the chimeric protein of any one of [1] to [5], wherein the mouse     Fcγ receptor is mouse Fcγ receptor 3; -   [7] the chimeric protein of any one of [1] to [5], wherein the mouse     Fcγ receptor is mouse Fcγ receptor 4; -   [8] a gene encoding the chimeric protein of any one of [1] to [7]; -   [9] a vector comprising the gene of [8]; -   [10] a cell expressing the chimeric protein of any one of [1] to     [7]; -   [11] the cell of [10], wherein the cell is an NK cell; -   [12] the cell of [10] or [11], wherein the cell is a human-derived     cell; -   [13] a method for measuring the cytotoxic activity of an antibody,     wherein the method comprises the steps of:

(a) contacting a test antibody with a cell expressing an antigen to which the test antibody binds;

(b) contacting the test antibody of (a) with the cell of any one of [10] to [12]; and

(c) measuring the cytotoxic activity of the test antibody;

-   [14] the measurement method of [13], wherein the test antibody is a     mouse-derived antibody; -   [15] a method of screening for an antibody having cytotoxic     activity, wherein the method comprises the steps of:

(a) contacting a test antibody with a cell expressing an antigen to which the test antibody binds;

(b) contacting the test antibody of (a) with the cell of any one of [10] to [12];

(c) measuring the cytotoxic activity of the test antibody; and

(d) selecting an antibody having cytotoxic activity;

-   [16] the screening method of [15], wherein the test antibody is a     mouse-derived antibody; -   [17] use of the chimeric protein of any one of [1] to [7] for     measuring cytotoxic activity; -   [18] use of the cell of any one of [10] to [12] for measuring     cytotoxic activity; -   [19] use of the chimeric protein of any one of [1] to [7] for     screening for an antibody having cytotoxic activity; -   [20] use of the cell of any one of [10] to [12] for screening for an     antibody having cytotoxic activity.

Mode for Carrying Out the Invention

The present invention provides chimeric receptors comprising a mouse Fcγ receptor extracellular domain and a human Fcγ receptor transmembrane domain. The present invention also provides chimeric receptors comprising a mouse Fcγ receptor extracellular domain and a human γ chain transmembrane domain.

The chimeric receptors of the present invention are preferably receptors that exhibit the activity to transmit signals into cells when the Fc region of a mouse antibody is bound to the extracellular domain of the receptors.

The mouse Fcγ receptors used in the present invention are not particularly limited, and any mouse Fcγ receptor may be used. The receptors are preferably mouse Fcγ receptor 3 (FcγR3) and mouse Fcγ receptor 4 (FcγR4).

Comparing the expression pattern of mouse FcγR3 and mouse FcγR4, mouse FcγR3 is expressed mainly in NK cells, and mouse FcγR4 is expressed in macrophages and neutrophils (Immunity 2005, 23, 41). Mouse FcγR3 binds to mouse IgG1, mouse IgG2a, and mouse IgG2b, while mouse FcγR4 does not bind to mouse IgG1 (Immunity 2005, 23, 4 1; Science 2005, 310, 1510). Therefore, when evaluating the ADCC activity of various types of mouse antibodies, mouse FcγR3, which allows measurement using even mouse IgG1, is preferably used.

Known nucleotide sequences of the DNAs encoding mouse Fcγ receptors, and known amino acid sequences thereof can be used. For example, as the nucleotide sequences of DNAs encoding mouse Fcγ receptor 3 and mouse Fcγ receptor 4, and the amino acid sequences thereof, the sequences of SEQ ID NO: 1 (mouse Fcγ receptor 3 nucleotide sequence), SEQ ID NO: 2 (mouse Fcγ receptor 3 amino acid sequence), SEQ ID NO: 3 (mouse Fcγ receptor 4 nucleotide sequence), and SEQ ID NO: 4 (mouse Fcγ receptor 4 amino acid sequence) may be used. Within the amino acid sequence of SEQ ID NO: 2, amino acid positions 31 to 212 correspond to the extracellular domain of mouse Fcγ receptor 3. Within the amino acid sequence of SEQ ID NO: 4, amino acid positions 19 to 201 correspond to the extracellular domain of mouse Fcγ receptor 4.

The extracellular domain of a receptor may be the entire extracellular domain, or may be a portion thereof. The entire extracellular domain is preferably used, since the receptor activity, such as the activity to bind to an antibody Fc region, can be appropriately retained. When using a portion of the extracellular domain of a receptor, the portion preferably retains the activity to bind to an antibody Fc region. The mouse Fcγ receptor extracellular domain used for the chimeric receptors of the present invention may include amino acid substitutions, deletions, insertions, and/or additions, as long as the domains have the ability to bind to an antibody Fc region. A method of introducing mutations into a protein is well-known to those skilled in the art as a method for preparing proteins that are functionally equivalent to a certain protein. For example, those skilled in the art can prepare such proteins using site-directed mutagenesis (Hashimoto-Gotoh, T. et al. (1995) Gene 152, 271-275; Zoller, M J, and Smith, M. (1983) Methods Enzymol. 100, 468-500; Kramer, W. et al. (1984) Nucleic Acids Res. 12, 9441-9456; Kramer W, and Fritz H J (1987) Methods. Enzymol. 154, 350-367; Kunkel, T A (1985) Proc. Natl. Acad. Sci. USA. 82, 488-492; Kunkel (1988) Methods Enzymol. 85, 2763-2766) and such. The number of mutated amino acids in such mutants is generally 50 amino acids or less, preferably 30 amino acids or less, more preferably 20 amino acids or less, still more preferably ten amino acids or less, and yet more preferably five amino acids or less.

It is desirable that the amino acid residues are mutated into other amino acids in which the properties of the amino acid side chains are conserved. For example, amino acids are categorized as follows depending on the side chain properties: hydrophobic amino acids (A, I, L, M, F, P, W, Y, and V); hydrophilic amino acids (R, D, N, C, E, Q, G, H, K, S, and T); amino acids having aliphatic side chains (G, A, V, L, I, and P); amino acids having hydroxyl-containing side chains (S, T, and Y); amino acids having sulfur atom-containing side chains (C and M); amino acids having carboxylic acid- and amide-containing side chains (D, N, E, and Q); amino acids having base-containing side chains (R, K, and H); and amino acids having aromatic ring-containing side chains (H, F, Y, and W) (amino acids are represented by one-letter codes in parentheses).

Polypeptides having a modified amino acid sequence, in which one or more amino acid residues in a certain amino acid sequence is deleted, added, and/or substituted with other amino acids, are known to retain the biological activity of the original polypeptides (Mark, D. F. et al., Proc. Natl. Acad. Sci. USA (1984) 81, 5662-5666; Zoller, M. J. & Smith, M. Nucleic Acids Research (1982) 10, 6487-6500; Wang, A. et al., Science 224, 1431-1433; Dalbadie-McFarland, G. et al., Proc. Natl. Acad. Sci. USA (1982) 79, 6409-6413).

The mouse Fcγ receptor extracellular domain used for the chimeric receptors of the present invention may be a polypeptide having high homology to a mouse Fcγ receptor (for example, mouse Fcγ receptor 3, mouse Fcγ receptor 4, etc.), as long as the polypeptide has the ability to bind to an antibody Fc region. In the present invention, “high homology” of a polypeptide generally refers to a sequence identity of 70% or higher, preferably 80% or higher, more preferably 90% or higher, and still more preferably 95% or higher. Polypeptide homology can be determined by the algorithm described in literature (Wilbur, W. J. and Lipman, D. J. Proc. Natl. Acad. Sci. USA (1983) 80, 726-730).

To isolate a DNA encoding a polypeptide having high homology to a mouse Fcγ receptor, hybridization reaction may be usually performed under stringent conditions. Stringent hybridization conditions can be selected appropriately by those skilled in the art. For example, hybridization may be performed by conducting overnight prehybridization at 42° C. in a hybridization solution containing 25% formamide, or 50% formamide under more stringent conditions; 4×SSC; 50 mM Hepes pH 7.0; 10× Denhardt's solution; and 20 μg/mL denatured salmon sperm DNA, then adding a labeled probe, and then incubating the solution overnight at 42° C. The subsequent washing can be carried out using washing solution and temperature conditions of “1×SSC, 0.1% SDS, 37° C.” or such, “0.5×SSC, 0.1% SDS, 42° C.” or such for more stringent conditions, or “0.2×SSC, 0.1% SDS, 65° C.” or such for even more stringent conditions. The more stringent the washing conditions for hybridization are, the higher the homology of an isolated DNA to the probe sequence is expected to be. However, the above-mentioned combinations of SSC, SDS, and temperature conditions are examples, and those skilled in the art can suitably combine the above-mentioned factors and/or other factors (for example, probe concentration, probe length, hybridization reaction time, etc.) that determine hybridization stringency, to realize similar stringency.

The homology of a DNA isolated is at least 50% or more, more preferably 70% or more, and even more preferably 90% or more (for example, 95%, 96%, 97%, 98%, 99%, or more), in terms of overall amino acid sequence identity. Programs such as BLASTN (nucleic acid level) and BLASTX (amino acid level) (Altschul et al. J. Mol. Biol., 215:403-410, 1990) can be used to determine the sequence homology. These programs are based on the BLAST algorithm by Karlin and Altschul (Proc. Natl. Acad. Sci. USA, 87:2264-2268, 1990; Proc. Natl. Acad. Sci. USA, 90: 5873-5877, 1993). When nucleotide sequences are analyzed by BLASTN, parameters are set, for example, at score=100 and wordlength=12. When amino acid sequences are analyzed by BLASTX, parameters are set, for example, at score=50 and wordlength=3. When amino acid sequences are analyzed using the Gapped BLAST program, the analysis can be performed as described by Altschul et al. (Nucleic Acids Res. 25: 3389-3402, 1997). When using the BLAST and Gapped BLAST programs, the default parameters of each program are utilized. Specific procedures for these analytical methods are known.

Alternatively, a DNA encoding a polypeptide highly homologous to a mouse Fcγ receptor can be isolated by utilizing a gene amplification method such as polymerase chain reaction (PCR) using primers that are synthesized based on the sequence information of DNAs encoding mouse Fcγ receptors (SEQ ID NOs: 1 and 3).

In the chimeric receptors of the present invention, a human Fcγ receptor transmembrane domain or a human γ chain transmembrane domain is used as the transmembrane domain.

The human Fcγ receptor used in the present invention is not particularly limited and may be any human Fcγ receptor; however, human Fcγ receptor 3 is preferred. Known nucleotide sequences of the DNAs encoding human Fcγ receptors, and known amino acid sequences thereof can be used. For example, as the nucleotide sequence of the DNA encoding human Fcγ receptor 3 and the amino acid sequence thereof, the sequences of SEQ ID NO: 5 (human Fcγ receptor 3 nucleotide sequence) and SEQ ID NO: 6 (human Fcγ receptor 3 amino acid sequence) may be used. Within the amino acid sequence of SEQ ID NO: 6, amino acid positions 207 to 229 correspond to the transmembrane domain.

Furthermore, the nucleotide sequence of the DNA encoding the human γ chain and the amino acid sequence thereof are known. For example, the sequences of SEQ ID NO: 7 (human y chain nucleotide sequence) and SEQ ID NO: 8 (human γ chain amino acid sequence) can be used. In the amino acid sequence of SEQ ID NO: 8, amino acid positions 24 to 44 correspond to the transmembrane domain.

The transmembrane domain of a receptor may be the entire transmembrane domain or may be a portion thereof. The entire transmembrane domain is preferably used, since receptor activity such as signal transduction activity can be appropriately retained. When using a portion of the transmembrane domain, the portion preferably retains the signal transduction activity. The transmembrane domain used for the chimeric receptors of the present invention may include amino acid substitutions, deletions, insertions, and/or additions. The transmembrane domain used in the present invention may be a polypeptide highly homologous to such a transmembrane domain. Amino acid substitutions, deletions, insertions, and additions, and highly homologous polypeptides are as described above. Polypeptides with amino acid substitutions, deletions, insertions, and/or additions, and highly homologous polypeptides preferably retain the signal transduction activity of the transmembrane domain.

Preferably, chimeric receptors of the present invention, which comprise a mouse Fcγ receptor extracellular domain and a human Fcγ receptor transmembrane domain, or comprise a mouse Fcγ receptor extracellular domain and a human γ chain transmembrane domain, further comprise an intracellular domain.

An intracellular domain used for the chimeric receptors of the present invention is not particularly limited, and may be any type of intracellular domain. When a human Fcγ receptor transmembrane domain is used as the transmembrane domain, a human Fcγ receptor intracellular domain is preferably used as the intracellular domain. When the human γ chain is used as the transmembrane domain, a human γ chain intracellular domain is preferably used as the intracellular domain.

As the human Fcγ receptor 3 intracellular domain, for example, the region of amino acid positions 230 to 254 in the amino acid sequence of SEQ ID NO: 6 can be used. As the human γ chain intracellular domain, for example, the region of amino acid positions 45 to 86 in the amino acid sequence of SEQ ID NO: 8 can be used.

The intracellular domain of a receptor may be the entire intracellular domain, or may be a portion thereof. The entire intracellular domain is preferably used, since the receptor activity such as signal transduction activity can be appropriately retained. When using a portion of the intracellular domain, the portion preferably retains the signal transduction activity. The intracellular domain used for the chimeric receptors of the present invention may comprise amino acid substitutions, deletions, insertions, and additions. The intracellular domain used in the present invention may be a polypeptide highly homologous to such an intracellular domain. Amino acid substitutions, deletions, insertions, and additions, and highly homologous polypeptides are as described above. Polypeptides with amino acid substitutions, deletions, insertions, and/or additions, and highly homologous polypeptides preferably retain the signal transduction activity of the intracellular domain.

In a preferred embodiment, the chimeric receptors of the present invention include the chimeric receptors of (a) to (f) below:

(a) a chimeric receptor comprising the amino acid sequence of SEQ ID NO: 10 (a chimeric receptor comprising the mouse FcγR3 extracellular domain and the human FcγR3 transmembrane domain and intracellular domain; “mouse FcγR3/human FcγR3”);

(b) a chimeric receptor comprising the amino acid sequence of SEQ ID NO: 12 (a chimeric receptor comprising the mouse FcγR3 extracellular domain and the human γ chain transmembrane domain and intracellular domain; “mouse FcγR3/human γ chain”);

(c) a chimeric receptor comprising the amino acid sequence of SEQ ID NO: 14 (a chimeric receptor comprising the mouse FcγR4 extracellular domain and the human FcγR3 transmembrane domain and intracellular domain; “mouse FcγR4/human FcγR3”);

(d) a chimeric receptor comprising the amino acid sequence of SEQ ID NO: 16 (a chimeric receptor comprising the mouse FcγR4 extracellular domain and the human γ chain transmembrane domain and intracellular domain; “mouse FcγR4/human γ chain);

(e) receptors in which one or more amino acids are substituted, deleted, added, and/or inserted in the chimeric receptors of (a) to (d) above, which are chimeric receptors having activity equivalent to that of the chimeric receptors of (a) to (d).

(f) receptors having amino acid sequences that are highly homologous to the amino acid sequences of the chimeric receptors of (a) to (d) above, which are chimeric receptors having activity equivalent to that of the chimeric receptors of (a) to (d).

Amino acid substitutions, deletions, additions, and insertions, and high homology are as described above.

In the present invention, “having ‘activity equivalent to’ that of the chimeric receptors of (a) to (d)” refers to having equivalent biological or biochemical activity. Examples of the biological or biochemical activity of the chimeric receptors of the present invention include the ability to bind to the Fc region of a mouse antibody or the ability to transmit ADCC signals.

The activity of the chimeric receptors of the present invention to bind to a mouse antibody Fc region can be measured by methods known to those skilled in the art, such as the ELISA, BIACORE, and Western blotting methods.

Whether or not the chimeric receptors of the present invention transmit ADCC signals can be determined by methods known to those skilled in the art. For example, it can be determined by using a chimeric receptor-expressing human NK cells (human NK92 cells or such) as effector cells, contacting the NK cells with a mouse antibody bound to an antigen expressed on target cells, and measuring the ADCC activity. More specifically, it can be determined by the methods described below, or by the methods described in the Examples of the present invention.

DNAs encoding the chimeric receptors of the present invention, and transcriptional RNA products of the DNAs are also included in the present invention. The DNAs encoding the chimeric receptors of the present invention can be prepared by methods known to those skilled in the art. For example, DNAs encoding the extracellular domain and the transmembrane domain can be prepared by making a cDNA library from cells expressing a receptor from which the extracellular domain or the transmembrane domain of the present invention is derived, and then performing hybridization using a portion of a known DNA sequence as the probe. DNAs encoding the chimeric receptors of the present invention can be prepared by linking the respective DNAs prepared.

Examples of the nucleotide sequences of the DNAs encoding the chimeric receptors of the present invention include the nucleotide sequences of SEQ ID NO: 9 (mouse FcγR3/human FcγR3), SEQ ID NO: 11 (mouse FcγR3/human γ chain), SEQ ID NO: 13 (mouse FcγR4/human FcγR3), and SEQ ID NO: 15 (mouse FcγR4/human γ chain).

The prepared DNA encoding a chimeric receptor of the present invention is ligated to a vector DNA. A recombinant vector is thus produced, then introduced into Escherichia coli or such, a colony is selected, and a desired recombinant vector can be prepared. As the vector DNA for carrying a DNA, known vector DNAs (for example, pUC 19 and pBluescript) can be used. Known E. coli strains (for example, DH5α and JM109) may be used. The nucleotide sequence of a DNA of interest can be identified by a known method, such as dideoxynucleotide chain termination. Alternatively, an automatic sequencing apparatus can be used.

DNAs of the present invention may be designed to have nucleotide sequences that are expressed more efficiently considering the codon usage frequency in the host used for expression (Grantham R. et al. Nucleic Acids Res. (1981) 9, r43-74). DNAs of the present invention can be modified by commercially available kits or known methods. Examples of the modification include digestion with restriction enzymes, insertion of a synthetic oligonucleotide or an appropriate DNA fragment, addition of a linker, and insertion of the initiation codon and/or a stop codon.

A chimeric receptor of the present invention can be expressed by producing an expression vector comprising a DNA encoding the chimeric receptor linked to an expression regulatory region such as a promoter. This expression vector is used to transform a host cell to express the chimeric receptor in the cell. Enhancers or such may be included in the vector.

Promoters that are useful for expression in host cells include virus promoters such as cytomegalovirus, retrovirus, polyomavirus, adenovirus, and SV40 promoters, and promoters derived from mammalian cells.

Selection marker genes can be included in the expression vectors for gene transfer into host cells.

Gene transfer into host cells can be carried out by known methods such as the calcium phosphate method, the lipofection method, and the electroporation method.

The present invention provides vectors comprising a DNA encoding a chimeric receptor of the present invention. Vectors used in the present invention are not particularly limited, and may be any vector. A vector can be appropriately selected by those skilled in the art. For example, pCOS1 (WO98/13388), pME18S (Med. Immunol. 20, 27-32 (1990)), pEF-BOS (Nucleic Acids Res. 18, 5322 (1990)), pCDM8 (Nature 329, 840-842 (1987)), pRSV-neo, pcDNAI/Amp (Invitrogen), pcDNAI, pAMoERC3Sc, pCDM8 (Nature 329, 840 (1987)), pAGE107 (Cytotechnology 3, 133 (1990)), pREP4 (Invitrogen), pAGE103 (J. Biochem. 101, 1307 (1987)), pAMoA, pAS3-3, pCAGGS (Gene 108, 193-200 (1991)), pBK-CMV, pcDNA3.1 (Invitrogen), pZeoSV (Stratagene), and such may be used.

The present invention relates to cells expressing a chimeric receptor of the present invention. Cells expressing a chimeric receptor of the present invention can be produced by methods known to those skilled in the art. For example, the cells can be produced by introducing the above-mentioned vectors of the present invention into the cells. Cells used in the present invention are not particularly limited, and may be of any type. However, the cells are preferably effector cells, more preferably NK cells, and particularly preferably NK92 cells. Cells used in the present invention are preferably human-derived cells. In particular, human-derived NK cells are preferred. Known human NK cells may be used, or human NK cells may be produced and used. Cells used in the present invention may be cells expressing the human γ chain, or cells that do not express the human γ chain. However, cells expressing the human γ chain are preferred. When using cells that do not express the human γ chain or cells with low expression level of the human γ chain, expression of the human γ chain can be forced by introducing a gene encoding the human γ chain.

The present invention provides methods of measuring the cytotoxic activity of antibodies using a chimeric receptor of the present invention.

The cytotoxic activity can be measured using a chimeric receptor of the present invention in a manner similar to conventional cytotoxic activity measurements.

For example, the measurements can be performed by methods comprising the steps of:

-   (a) contacting a test antibody with a cell expressing an antigen to     which the test antibody binds; -   (b) contacting the test antibody of (a) with a cell expressing a     chimeric receptor of the present invention; and -   (c) measuring the cytotoxic activity of the test antibody.

In the present invention, “measurements” include quantitative and qualitative measurements. Examples of qualitative measurements include, for example, measurement only for the presence or absence of cytotoxic activity in a test antibody, measurement to see whether or not a test antibody has cytotoxic activity above a certain level, and measurement that compares the cytotoxic activity of a test antibody with that of control antibodies (positive control, negative control, etc.). On the other hand, examples of quantitative detection include measurement of the absolute or relative value of the cytotoxic activity of a test antibody, and evaluation of the usefulness of a test antibody as a pharmaceutical.

The present invention also provides methods of screening for an antibody having cytotoxic activity, which use a chimeric receptor of the present invention.

Specifically, screening for an antibody having cytotoxic activity can be performed by methods comprising the steps of:

-   (a) contacting a test antibody with a cell expressing an antigen to     which the test antibody binds; -   (b) contacting the test antibody of (a) with a cell expressing a     chimeric receptor of the present invention; -   (c) measuring the cytotoxic activity of the test antibody; and -   (d) selecting an antibody having cytotoxic activity.

The screening methods of the present invention may be any method including screening for antibodies having cytotoxic activity from test antibodies for which the presence or absence of cytotoxic activity is unknown; screening for antibodies having high cytotoxic activity from test antibodies having cytotoxic activity; and screening for antibodies that are useful as pharmaceuticals from test antibodies having cytotoxic activity, or from test antibodies for which the presence or absence of the cytotoxic activity is unknown.

In the methods of the present invention, the cytotoxic activity measured is generally antibody-dependent cell-mediated cytotoxicity (ADCC activity).

The test antibodies used in the methods of the present invention are not particularly limited. While any type of antibody may be used, the test antibodies generally have a region that can bind to the extracellular domain of a chimeric receptor of the present invention. Preferred examples of the test antibodies include mouse antibodies, and antibodies having an Fc region derived from a mouse antibody. The amino acid sequence of an Fc region of the test antibodies can be modified, and so can the sugar chain(s).

Antigens to which the test antibodies bind are not particularly limited, but are preferably membrane proteins. Examples of membrane proteins include receptors, transport proteins, ion channels, and cell membrane antigens.

In the present invention, preferred examples of antigens to which the test antibodies bind include disease-related antigens. Disease-related antigens are antigens that have been demonstrated to be expressed in a specific disease, and are preferably antigens whose expression level increases under a specific disease state compared to normal conditions. Examples of disease-related antigens include proteins highly expressed in cancers, and proteins highly expressed in autoimmune diseases.

A cell expressing the antigen can be any cell, and may be a cell that inherently expresses the antigen to which a test antibody binds, or a cell in which expression of the antigen is forced by introducing a gene encoding the antigen. Preferred examples of antigens used in the methods of the present invention include cancer cells, or autoimmune disease-related cells such as B cells.

Generally, in the methods of the present invention, a test antibody is contacted with a cell expressing an antigen to which the test antibody binds, and then the test antibody bound to the cell expressing the antigen is contacted with a cell expressing a chimeric receptor of the present invention. However, the order in which the test antibody, the cell expressing the antigen, and the cell expressing the chimeric receptor of the present invention are contacted is not limited to the above-described order. The test antibody, the cell expressing the antigen, and the cell expressing the chimeric receptor of the present invention may be contacted simultaneously. Alternatively, after contacting the test antibody with the cell expressing the chimeric receptor of the present invention, the cell expressing the antigen may be contacted with them.

Whether or not an antibody has ADCC activity can be determined by known methods (for example, Current Protocols in Immunology, Chapter 7. Immunologic studies in humans, Editor, John E, Coligan et al., John Wiley & Sons, Inc., (1993)).

Specifically, the determination can be carried out by the following method.

First, effector cells and target cells are prepared.

(1) Preparation of Effector Cells

The effector cells can be prepared by adjusting the concentration of chimeric receptor-expressing cells of the present invention to 5×10⁶ cells/mL.

(2) Preparation of Target Cells

The target cells can be radioactively labeled by incubating cells expressing an antigen to which a test antibody binds with 0.2 mCi of sodium chromate-⁵¹Cr (manufactured by GE Healthcare Bio-Sciences) in RPMI 1640 medium containing 10% FBS for one hour at 37° C. After radioactive labeling, cells are washed three times in RPMI 1640 medium containing 10% FBS. The target cells can be prepared by adjusting the cell concentration to 2×10⁵ cells/mL.

The intensity of ADCC activity can be measured by the method described below. Fifty μL each of the target cells and the test antibody are added to a 96-well U-bottomed plate (manufactured by Becton Dickinson), and reacted for 15 minutes on ice. Thereafter, 100 μL of the cells expressing a chimeric receptor of the present invention are added as the effector cells, and incubated in a carbon dioxide gas incubator for four hours. The final concentration of the antibody is adjusted to 0 or 10 μg/mL. After incubation, 100 μL of the supernatant is collected, and the radioactivity is measured by a gamma counter (COBRAII AUTO-GAMMA, MODEL D5005, manufactured by Packard Instrument Company). Using the values obtained, the cytotoxic activity (%) can be calculated according to the equation: (A−C)/(B−C)×100, wherein A represents the radioactivity (cpm) in each sample, B represents the radioactivity (cpm) in a sample to which 1% NP-40 (manufactured by Nacalai Tesque) has been added, and C represents the radioactivity (cpm) of a sample containing only the target cells.

The antibodies having cytotoxic activity that are selected by the screening methods of the present invention can be used as pharmaceuticals for treating or preventing various types of diseases. For example, the antibodies may be used as therapeutic agents or preventive agents against diseases such as cancers or autoimmune diseases.

The present invention further provides methods of producing antibodies having cytotoxic activity, which use the chimeric receptors of the present invention. Specifically, the production can be carried out by methods comprising the steps of:

-   (a) contacting a test antibody with a cell expressing an antigen to     which the test antibody binds; -   (b) contacting the test antibody of (a) with a cell expressing a     chimeric receptor of the present invention; -   (c) measuring the cytotoxic activity of the test antibody; -   (d) selecting an antibody having cytotoxic activity; -   (e) producing an expression vector comprising a gene encoding the     antibody selected; -   (f) transfecting the vector of (e) into host cells; -   (g) culturing the host cells of (f); and -   (h) collecting the antibody from the host cells cultured in (g).

The gene encoding the selected antibody may be a gene encoding an antibody having an amino acid sequence that is identical to the full amino acid sequence of the selected antibody, or a gene encoding an antibody having an amino acid sequence partially identical to that of the selected antibody. Preferred examples of an antibody having an amino acid sequence partially identical to that of the selected antibody include antibodies having variable regions identical to those of the selected antibody, and antibodies having complementarity determining regions (CDRs) identical to those of the selected antibody. Methods for substituting regions other than variable regions or CDRs with sequences derived from other antibodies are known (see, European Patent Publication No. EP 239,400, and International Patent Publication No. WO 96/02576).

When using these antibodies as pharmaceuticals for humans or mammals, besides administering them directly as they are to patients, they can be administered as formulations produced by known preparation methods. For example, as necessary, the antibodies may be administered orally as tablets, capsules, or such; or parenterally in the form of injections of sterile solutions or suspensions prepared with water or other pharmaceutically acceptable liquids. For example, the antibodies may be formulated by appropriately combining them with pharmaceutically acceptable carriers or media, more specifically, sterilized water or physiological saline solutions, vegetable oils, emulsifiers, suspending agents, surfactants, stabilizers, flavoring agents, vehicles, preservatives, binding agents, and such, and mixing them into a unit dosage form required for generally accepted pharmaceutical practice. The amount of active ingredient in the formulation is such that appropriate doses within indicated ranges are achieved. Additives that can be mixed into tablets and capsules include, for example, binding agents such as gelatin, cornstarch, tragacanth gum, and gum arabic; excipients such as crystalline cellulose; swelling agents such as cornstarch, gelatin, alginic acid; lubricants such as magnesium stearate; sweeteners such as sucrose, lactose, and saccharine; and flavoring agents such as peppermint and Gaultheria adenothrix oils, and cherry. When the unit dosage form is a capsule, liquid carriers such as oils and fats can be further included in the above-indicated materials. Sterile compositions to be injected can be formulated using a vehicle such as distilled water for injection, according to standard formulation practice.

Aqueous solutions for injections include, for example, physiological saline and isotonic solutions containing glucose or other adjunctive agents such as D-sorbitol, D-mannose, D-mannitol, and sodium chloride. The solutions may also be combined with appropriate solubilizing agents such as alcohol, more specifically, ethanol, polyalcohol such as propylene glycol or polyethylene glycol, or non-ionic surfactants such as Polysorbate 80 or HCO-50.

Oil solutions include sesame oils and soybean oils, and can be combined with solubilizing agents such as benzyl benzoate or benzyl alcohol. Injection solutions may also be formulated with buffers such as phosphate buffers or sodium acetate buffers; analgesics such as procaine hydrochloride; stabilizers such as benzyl alcohol or phenol; or anti-oxidants. The solutions prepared are typically aliquoted into appropriate ampules.

Administration to patients may be performed, for example, by intra-arterial injection, intravenous injection, or subcutaneous injection, alternatively, by intranasal, transbronchial, intramuscular, transdermal, or oral administration, using methods known to those skilled in the art.

All prior art references cited herein are incorporated by reference into this description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the results of measuring DSG3 expression in DSG3-Ba/F3 cells by flow cytometry. The results are indicated by a thick line for DSG3 monoclonal antibody (R&D Systems), a solid line for the negative control antibody (mouse IgG2a, Becton Dickinson), and a dashed line for no primary antibody.

FIG. 2 shows the results of measuring the ADCC activity when mouse spleen cells were used as effector cells.

FIG. 3 shows the results of measuring the ADCC activity when mouse FcγR4/human FcγR3-expressing and mouse FcγR4/human γ-expressing NK92 cells were used as effector cells.

FIG. 4 shows the results of measuring the ADCC activity when mouse FcγR3/human γ-expressing NK92 cells were used as effector cells.

FIG. 5 shows the results of measuring the ADCC activity when mouse FcγR3/human FcγR3-expressing NK92 cells were used as effector cells.

FIG. 6 shows the results of measuring the ADCC activity when human FcγR3-expressing NK92 cells were used as effector cells.

FIG. 7 shows the results of measuring the ADCC activity of anti-claudin3 monoclonal antibodies.

EXAMPLES

Herein below, the present invention will be specifically described with reference to the Examples, but it is not to be construed as being limited thereto.

Example 1 Establishment of FcγR-Expressing NK92 Cell Lines 1-1) Construction of Mouse FcγR4 Expression Vector

Using mouse spleen cDNA (Clontech) as a template, the mouse FcγR4 gene was amplified by PCR utilizing a sense primer containing an EcoRI restriction enzyme sequence (mFcR4-EcoRI-F, SEQ ID NO: 17) and an antisense primer containing a NotI restriction enzyme sequence (mFcR4-NotI-R, SEQ ID NO: 18). After treatment with the EcoRI and NotI restriction enzymes, the amplified product was cloned into the EcoRI-NotI site of the pMCDN plasmid for expression in mammalian cells to produce pMCDN/mFcR4. The pMCDN vector, into which the neomycin resistance gene and the DHFR gene are inserted, enables induced expression under the control of the mouse CMV promoter (Accession No. U68299). The nucleotide sequence cloned was determined by sequencing using an AB13730 DNA sequencer. The nucleotide sequence and the amino acid sequence of mouse FcγR4 are shown in SEQ ID NOs: 3 and 4, respectively. Compared to the known sequence (NM_(—)144559), the nucleotide at position 422 had been changed from C to T in the sequence obtained; therefore, the amino acid at position 141 had been changed from serine to leucine.

1-2) Construction of Mouse FcγR3 Expression Vector

Using mouse spleen cDNA (Clontech) as a template, the mouse FcγR3 gene was amplified by PCR utilizing a sense primer containing an EcoRI restriction enzyme sequence (mFcR3-EcoRI-F, SEQ ID NO: 19) and an antisense primer containing a Not I restriction enzyme sequence (mFcR3-NotI-R, SEQ ID NO: 20). After treatment with the EcoRI and NotI restriction enzymes, the amplified product was cloned into the EcoRI-NotI site of the pMCDN plasmid to produce pMCDN/mFcR3. The nucleotide sequence cloned was determined by sequencing using an ABI3730 DNA sequencer. The nucleotide sequence and the amino acid sequence of mouse FcγR3 are shown in SEQ ID NOs: 1 and 2, respectively.

1-3) Construction of Mouse FcγR4/Human FcγR3 Chimeric Expression Vector

Using the pMCDN/mFcR4 plasmid, into which the mouse FcγR4 gene has been inserted, as a template, the extracellular domain of mouse FcγR4 was amplified by PCR utilizing a sense primer (mFcR4-EcoRI-F) and an antisense primer (m4h3-mR, SEQ ID NO: 21). Then, using the pMCDN/hFcR3 plasmid, which was prepared by inserting the human FcγR3 gene (nucleotide sequence: SEQ ID NO: 5; amino acid sequence: SEQ ID NO: 6) into pMCDN, as a template, the transmembrane domain and intracellular domain of human FcγR3 were amplified by PCR utilizing a sense primer (m4h3-hF, SEQ ID NO: 22) and an antisense primer (vector primer: pMCM-R1, SEQ ID NO: 23). After mixing these amplification products in an equal amount, the products were further amplified using the mFcR4-EcoRI-F primer and pMCM-R1 primer, treated with the EcoRI and NotI restriction enzymes, and then inserted into the EcoRI-NotI site of the pMCDN plasmid to construct the mouse FcγR4/human FcγR3 chimeric (mouse FcγR4/human FcγR3) expression vector (pMCDN/mFcR4-hFcR3). The nucleotide sequence cloned was determined by sequencing using an ABI3730 DNA sequencer. The nucleotide sequence and the amino acid sequence of mouse FcγR4/human FcγR3 are shown in SEQ ID NOs: 13 and 14, respectively.

1-4) Construction of Mouse FcγR4/Human γ Chain Chimeric Expression Vector

Using the pMCDN/mFcR4 plasmid, into which the mouse FcγR4 gene has been inserted, as a template, the extracellular domain of mouse FcγR4 was amplified by PCR utilizing a sense primer (mFcR4-EcoRI-F) and an antisense primer (m4hG-mR, SEQ ID NO: 24). Then, using human spleen cDNA (Clontech) as a template, the two amino acids of the extracellular domain, the transmembrane domain, and the intracellular domain of human γ chain (nucleotide sequence: SEQ ID NO: 7; amino acid sequence: SEQ ID NO: 8) were amplified by PCR utilizing a sense primer (m4hG-hF, SEQ ID NO: 25) and an antisense primer (m4hG-hR, SEQ ID NO: 26). After mixing these amplification products in an equal amount, the products were further amplified using the mFcR4-EcoRI-F primer and m4hG-hR primer, treated with the EcoRI restriction enzyme, and then inserted into the EcoRI-EcoRV site of the pMCDN plasmid to construct the mouse FcγR4/human γ chain chimeric (mouse FcγR4/human γ) expression vector (pMCDN/mFcR4-hG). The nucleotide sequence cloned was determined by sequencing using an ABI3730 DNA sequencer. The nucleotide sequence and the amino acid sequence of mouse FcγR4/human γ are shown in SEQ ID NOs: 15 and 16, respectively.

1-5) Construction of Mouse FcγR3/Human FcγR3 Chimeric Expression Vector

Using the pMCDN/mFcR3 plasmid, into which the mouse FcγR3 gene has been inserted, as a template, the extracellular domain of mouse FcγR3 was amplified by PCR utilizing a sense primer (mFcR3-EcoRI-F) and an antisense primer (m3h3-mR, SEQ ID NO: 27). Then, using the pMCDN/mFcR4-hFcR3 plasmid, into which the mouse FcγR4/human FcγR3 gene has been inserted, as a template, the transmembrane domain and intracellular domain of human FcγR3 was amplified by PCR utilizing a sense primer (m3h3-hF, SEQ ID NO: 28) and an antisense primer (pMCM-R1). After mixing these amplification products in an equal amount, the products were further amplified using the mFcR3-EcoRI-F primer and pMCM-R1 primer, treated with EcoRI and NotI restriction enzymes, and then inserted into the EcoRI-NotI site of the pMCDN plasmid to construct the mouse FcγR3/human FcγR3 chimeric (mouse FcγR3/human FcγR3) expression vector (pMCDN/mFcR3-hFcR3). The nucleotide sequence cloned was determined by sequencing using an ABI3730 DNA sequencer. The nucleotide sequence and the amino acid sequence of mouse FcγR3/human FcγR3 are shown in SEQ ID NOs: 9 and 10, respectively.

1-6) Construction of Mouse FcγR3/Human γ Chain Chimeric Expression Vector

Using the pMCDN/mFcR3 plasmid, into which the mouse FcγR3 gene has been inserted, as a template, the extracellular domain of mouse FcγR3 was amplified by PCR utilizing a sense primer (mFcR3-EcoRI-F) and an antisense primer (m3hG-mR, SEQ ID NO: 29). Then, using the pMCDN/mFcR4-hG plasmid, into which the mouse FcγR4/human γ gene has been inserted, as a template, the two amino acids of the extracellular domain, the transmembrane domain, and the intracellular domain of human γ chain were amplified by PCR utilizing a sense primer (m3hG-hF, SEQ ID NO: 30) and an antisense primer (pMCM-R1). After mixing these amplification products in an equal amount, the products were further amplified using the mFcR3-EcoRI-F primer and pMCM-R1 primer, treated with the EcoRI and NotI restriction enzymes, and then inserted into the EcoRI-NotI site of the pMCDN plasmid to construct the mouse FcγR3/human γ chain chimeric (mouse FcγR3/human γ) expression vector (pMCDN/mFcR3-hG). The nucleotide sequence and the amino acid sequence of mouse FcγR3/human γ are shown in SEQ ID NOs: 11 and 12, respectively. 1-7) Introduction of FcγR expression vector into NK92 cell line NK92 cell lines that stably express mouse FcγR4/human FcγR3, mouse FcγR4/human γ, mouse FcγR3/human FcγR3, mouse FcγR3/human γ, and human FcγR3 were established by digesting the pMCDN/mFcR4-hFcR3, pMCDN/mFcR4-hG, pMCDN/mFcR3-hFcR3, pMCDN/mFcR3-hG, and pMCDN/hFcR3 plasmids with the PvuI restriction enzyme, then introducing the digested plasmids into the NK92 cell line (purchased from ATCC) by electroporation, and selecting the cells with 500 μg/mL Geneticin (Invitrogen). These NK92 cell lines were incubated in Alpha Minimum Essential Medium without ribonucleosides and deoxyribonucleosides with L-glutamine (Invitrogen) containing 500 μg/ml Geneticin, penicillin/streptomycin (Invitrogen), 100 U/ml recombinant human interleukin-2 (Peprotech), 10% fetal bovine serum (FBS, Invitrogen), 10% horse serum (Invitrogen), 0.11 mM 2-mercaptoethanol (Invitrogen), 0.2 mM inositol (Sigma), and 0.02 mM folic acid (Sigma).

Example 2 Preparation of Anti-Human Desmoglein 3 Antibody 2-1) Establishment of a Human Desmoglein 3 Expression Cell Line

A CHO cell line stably expressing human desmoglein 3 (DSG3) (DSG3-DG44) was established by digesting the pMCN/DSG3 plasmid for expression in mammalian cells, into which the DSG3 gene (nucleotide sequence: SEQ ID NO: 31; amino acid sequence: SEQ ID NO: 32) has been inserted, with the Pvu I restriction enzyme, then introducing the digested plasmid into the CHO DG44 cell line (Invitrogen) by electroporation, and selecting the cells with 500 μg/mL Geneticin. pMCN enables induced expression under the control of the mouse CMV promoter (Accession No. U68299), and is a vector into which the neomycin resistance gene has been inserted. DSG3-DG44 cells were incubated in CHO-S-SFM II medium (Invitrogen) containing 500 μg/mL Geneticin, HT supplement (Invitrogen), and penicillin/streptomycin.

2-2) Preparation of soluble Human Desmoglein 3/Mouse IgG2a-Fc Fusion Protein

Soluble human desmoglein 3/mouse IgG2a-Fc fusion protein (DSG3-Fc) was prepared as an immunizing antigen for producing anti-DSG3 antibodies. A gene constructed by linking the DSG3 extracellular domain (Met1-Leu616) with the mouse IgG2a constant region at the CpoI restriction enzyme sequence of the hinge region of the mouse IgG2a constant region (DSG3-Fc; nucleotide sequence: SEQ ID NO: 33; amino acid sequence: SEQ ID NO: 34) was cloned into the pMCDN plasmid to produce pMCDN/DSG3-Fc. A CHO cell line stably expressing DSG3-Fc (DSG3-Fc-DG44) was established by introducing the pMCDN/DSG3-Fc plasmid into DG44 cells by electroporation, and selecting the cells with 500 μg/mL of Geneticin. Then, DSG3-Fc was purified from the culture supernatant of DSG3-Fc-DG44. The culture supernatant was applied to a Hi Trap Protein G HP column (Cat. No. 17-0404-01, GE Healthcare Bio-Sciences), and after washing with a binding buffer (20 mM sodium phosphate, pH 7.0), elution was carried out using an elution buffer (0.1 M glycine-HCl, pH 2.7). The eluate was immediately neutralized by elution into a tube containing a neutralization buffer (1 M Tris-HCl (pH 9.0)). This eluate was subjected to gel filtration using Superdex 200 HR 10/30 (GE Healthcare Bio-Sciences) to replace the solvent with PBS. Purified DSG3-Fc was quantified using a DC protein assay kit (BIO-RAD) and converting to a concentration using bovine IgG included in the kit as standard.

2-3) Preparation of Anti-DSG3 Antibody

MRL/MpJUmmCrj-1pr/1pr mice (7- to 8-weeks old, purchased from Charles River Japan) were used as the animals for immunization. For the first immunization, 100 μg of DSG3-Fc was emulsified using Freund's complete adjuvant (Beckton Dickinson), and administered subcutaneously. Two weeks later, boosting immunization was carried out by emulsifying 50 μg of DSG3-Fc using Freund's incomplete adjuvant (Beckton Dickinson), and administering it subcutaneously. Thereafter, boosting immunizations were performed at one-week intervals for three times. For the final immunization, 50 μg of DSG3-Fc was administered into the tail vein. Four days after the final immunization, spleen cells were extirpated and mixed with mouse myeloma cells P3-X63Ag8U1 (purchased from ATCC) at 2:1 ratio, and cell fusion was carried out by addition of PEG 1500 (Roche Diagnostics). Then, RPMI 1640 medium (Invitrogen) was added, and then PEG 1500 was removed by centrifuging and removing the supernatant. The fused cells suspended in RPMI 1640 containing 10% FBS was seeded into a 96-well plate at 100 μL/well. On the following day, RPMI 1640 medium containing 10% FBS, 1× HAT media supplement (Sigma), and 0.5× BM-Condimed H1 Hybridoma cloning supplement (Roche Diagnostics) (HAT medium) was added at 100 μL/well. Two days later and three days later, half of the culture solution was replaced with HAT medium, and the day-7 culture supernatant was used for screening. The screening was performed by flow cytometry that detects binding to DSG3-DG44 cells. Positive clones obtained by this screening were monocloned by the limiting dilution method to establish a hybridoma that produces DF366, which is a monoclonal antibody that specifically binds to DSG3. This hybridoma was cultured in a HAT medium supplemented with Ultra-Low IgG FBS (Invitrogen) instead of FBS, and the DF366 antibody was purified from this culture supernatant using a Hi Trap Protein G HP column. The solvent was replaced with PBS using a PD-10 column (GE Healthcare Bio-Sciences). The concentration of the purified DF366 antibody was quantified using a DC protein assay kit. The isotype of the DF366 antibody was determined to be mouse IgG1κ by analysis using Isostrip (Roche Diagnostics).

Binding of the DF366 antibody to DSG3-DG44 cells was detected by flow cytometry. 5×10⁴ cells of DSG3-DG44 was reacted with 3 μg/mL of DF366 antibody on ice for 30 minutes, and then washed. Then, this was reacted with an FITC-labeled anti-mouse IgG antibody (Beckman Coulter) as the secondary antibody on ice for 30 minutes, washed, and then subjected to flow cytometry. FACS Calibur (Becton Dickinson) was used as the flow cytometer. The DF366 antibody bound to DSG3-DG44 cells, but not to the parental DG44 cells. Therefore, the DF366 antibody was confirmed to bind specifically to DSG3.

2-4) Preparation of Human IgG1 Chimeric DF366 Antibody (DF366c)

The H-chain variable region gene (nucleotide sequence: SEQ ID NO: 35; amino acid sequence: SEQ ID NO: 36) and the L-chain variable region gene (nucleotide sequence: SEQ ID NO: 37; amino acid sequence: SEQ ID NO: 38) of DF366 antibody were cloned from a hybridoma that produces the DF366 antibody. Then, these genes were ligated in frame with the nucleotide sequences of the H-chain constant region gene and L-chain (κ-chain) constant region gene of human IgG1. PCR was performed using a primer having the 5′-end nucleotide sequence of the H-chain variable region gene, a Kozak sequence, and an EcoRI restriction enzyme sequence, and an antisense primer having a sequence complementary to the 3′-end nucleotide sequence and a NheI restriction enzyme sequence. PCR was also performed using a primer having the 5′-end nucleotide sequence of the L-chain variable region gene, a Kozak sequence, and a BamHI restriction enzyme sequence, and an antisense primer having a sequence complementary to the 3′-end nucleotide sequence and the BsiWI restriction enzyme sequence. The amplification products obtained were treated with the EcoRI and NheI restriction enzymes, or BamHI and BsiWI restriction enzymes, and inserted into the EcoRI-NheI site or BamHI-BsiWI site of the human IgG1 chimeric antibody expression plasmid (pMCDN/G1k), to produce pMCDN/G1k-DF366. pMCDN/G1k was produced by cloning the H-chain constant region gene (nucleotide sequence: SEQ ID NO: 39; amino acid sequence: SEQ ID NO: 40) and the L-chain (κ-chain) constant region gene (nucleotide sequence: SEQ ID NO: 41; amino acid sequence: SEQ ID NO: 42) of human IgG1 cloned, into the pMCDN plasmid. The mouse H-chain variable region and the human H-chain constant region were linked by a NheI restriction enzyme sequence, and the mouse L-chain variable region and the human L-chain constant region were linked by the BsiWI restriction enzyme sequence.

The pMCDN/G1k-DF366 plasmid was introduced into DG44 cells by electroporation. The CHO DF366c-DG44 cells, which stably express the human IgG1 chimeric DF366 antibody (DF366c), were established by selection with 500 μg/mL of Geneticin. The DF366c antibody was purified from the culture supernatant of DF366c-DG44 using a Hi Trap rProtein A column (GE Healthcare Bio-Science). The solvent was replaced with PBS using a PD-10 column. The concentration of the DF366c antibody purified was quantified using a DC protein assay kit. The nucleotide sequence of the full-length DF366c antibody H-chain gene and the corresponding amino acid sequence are shown in SEQ ID NOs: 43 and 44, respectively. The nucleotide sequence of the full length DF366c antibody L-chain gene and the corresponding amino acid sequence are shown in SEQ ID NOs: 45 and 46, respectively.

Binding of the DF366c antibody to DSG3-DG44 cells and DG44 cells was detected by flow cytometry. 3×10⁴ cells were reacted with 10 μg/mL of DF366c antibody on ice for one hour, and then washed. Then, this was reacted with an FITC-labeled anti-human IgG antibody (Beckman Coulter) as the secondary antibody on ice for one hour, washed, and then subjected to flow cytometry. FACS Calibur (Becton Dickinson) was used as the flow cytometer. DF366c antibody bound to DSG3-DG44 cells, but not to the parental DG44 cells. Therefore, the DF366c antibody was confirmed to bind specifically to DSG3.

2-5) Preparation of Mouse IgG2a Chimeric DF366 Antibody (DF366m)

The nucleotide sequence of the DF366 antibody H-chain variable region gene was ligated in frame with the nucleotide sequence of the mouse IgG2a H-chain constant region gene. PCR was performed using a primer having the 5′-end nucleotide sequence of the H-chain variable region gene, a Kozak sequence, and an EcoRI restriction enzyme sequence, and an antisense primer having a cytosine residue attached to a sequence complementary to the 3′-end nucleotide sequence. The amplification product obtained was treated with the EcoRI restriction enzyme, and inserted into the EcoRI-NruI site of the mouse IgG2a chimeric H-chain expression plasmid (pMCD/G2a) to construct the mouse IgG2a chimeric DF366 antibody H chain expression vector (pMCD/G2a-DF366). pMCD/G2a was produced by cloning the mouse IgG2a H-chain constant region gene (nucleotide sequence: SEQ ID NO: 47; amino acid sequence: SEQ ID NO: 48) into the pMCD plasmid for expression in mammalian cells. The H-chain constant region was ligated to the H-chain variable region via the NruI restriction enzyme sequence. The pMCD vector, into which the DHFR gene is inserted, enables induced expression under the control of the mouse CMV promoter (Accession No. U68299).

The nucleotide sequence of the DF366 antibody L-chain variable region gene was ligated in frame with the nucleotide sequence of the L-chain (κ-chain) constant region gene of mouse IgG2a. PCR was performed using a primer having the 5′-end nucleotide sequence of the L-chain variable region gene, a Kozak sequence, and an EcoRI restriction enzyme sequence, and an antisense primer having “gcccg” residues attached to a sequence complementary to the 3′-end nucleotide sequence. The amplification product obtained was treated with the EcoRI restriction enzyme, and inserted into the EcoRI-NruI site of the mouse IgG2a chimeric L-chain (κ-chain) expression plasmid (pMCN/k) to construct the mouse IgG2a chimeric DF366 antibody L chain expression vector (pMCN/k-DF366). pMCN/k was produced by cloning the mouse IgG2a L-chain (κ-chain) constant region gene (nucleotide sequence: SEQ ID NO: 49; amino acid sequence: SEQ ID NO: 50) into the pMCN plasmid. The L-chain (κ-chain) constant region was ligated to the L-chain variable region via the NruI restriction enzyme sequence.

The pMCD/G2a-DF366 and pMCN/k-DF366 plasmids were introduced into DG44 cells by electroporation. The CHO DF366m-DG44 cells, which stably express the mouse IgG2a chimeric DF366 antibody (DF366m) were established by selection in a nucleic acid (HT supplement)-free medium containing 500 μg/mL of Geneticin. Subsequently, the DF366m antibody was purified from the culture supernatant of DF366m-DG44 using a Hi Trap Protein G HP column. The solvent was substituted with PBS using a PD-10 column. The concentration of the DF366m antibody purified was quantified using a DC Protein Assay kit. The DF366m antibody was subjected to flow cytometric analysis to confirm that the antibody specifically binds to DSG3 in the same way as the DF366c antibody. An FITC-labeled anti-mouse IgG antibody (Beckman Coulter) was used as the secondary antibody. The nucleotide sequence of the full-length DF366m antibody H-chain gene and the corresponding amino acid sequence are shown in SEQ ID NO: 51 and SEQ ID NO: 52, respectively. The nucleotide sequence of the full-length DF366m antibody L-chain gene and the corresponding amino acid sequence are shown in SEQ ID NO: 53 and SEQ ID NO: 54, respectively.

2-6) Production of Low-Fucose DF366 Antibody

The pMCDN/G1k-DF366 plasmid was introduced into a fucose transporter knockout CHO cell line (FTPKO-DXB11 cells, International Patent Publication Nos. WO 2006/067913 and WO 2006/067847) by electroporation. Low-fucose DF366c-DXB11, CHO cells stably expressing the low-fucose human IgG1 chimeric DF366 antibody (low-fucose DF366c), was established by selection with 500 μg/mL Geneticin. Subsequently, the low-fucose DF366c antibody was purified from the culture supernatant of low-fucose DF366c-DXB 11 using a Hi Trap rProtein A column. The solvent was substituted with PBS using a PD-10 column, and the antibody concentration was quantified using a DC Protein Assay kit.

The pMCD/G2a-DF366 and pMCN/k-DF366 plasmids were introduced into FTPKO-DXB11 cells by electroporation. Low-fucose DF366m-DXB11, CHO cells stably expressing the low-fucose mouse IgG2a chimeric DF366 antibody (low-fucose DF366m), was established by selection in a nucleic acid (HT supplement)-free medium containing 500 μg/mL of Geneticin. Subsequently, the low-fucose DF366m antibody was purified from the culture supernatant of low-fucose DF366m-DXB11 using a Hi Trap Protein G HP column. The solvent was substituted with PBS using a PD-10 column, and the antibody concentration was quantified using a DC Protein Assay kit.

Example 3 Measurement of the ADCC Activity of Anti-DSG3 Antibody 3-1) Establishment of the Target Cell Line

DSG3-Ba/F3, a Ba/F3 cell line stably expressing DSG3, was established by digesting, with the PvuI restriction enzyme, the pMCDN/DSG3 plasmid for expression in mammalian cells, into which the human desmoglein 3 (DSG3) gene (nucleotide sequence: SEQ ID NO: 31; amino acid sequence: SEQ ID NO: 32) has been inserted, then introducing the digested plasmid into Ba/F3 cells (purchased from RIKEN BioResource Center) by electroporation, and selecting the cells with 500 μg/mL Geneticin. DSG3-Ba/F3 cells were incubated using RPMI 1640 medium (Invitrogen) containing 500 μg/mL Geneticin, penicillin/streptomycin, recombinant mouse interleukin-3 (R&D Systems), and 10% FBS.

Expression of DSG3 was determined by flow cytometry (FIG. 1). Specifically, DSG3-Ba/F3 cells were reacted with 10 μg/mL of an anti-DSG3 monoclonal antibody (R&D Systems) or a negative control antibody (mouse IgG2a, Becton Dickinson) on ice for one hour, and then washed. Subsequently, this was reacted with a secondary antibody (FITC-labeled anti-mouse Ig antibody, Becton Dickinson) on ice for one hour, washed, and then analyzed using a flow cytometer (FACS Calibur, Becton Dickinson).

3-2) Methods for Measuring the ADCC Activity

RPMI 1640 medium containing penicillin/streptomycin and 10% FBS (RPMI medium) was used for the experiment. 1×10⁶ cells of the DSG3-Ba/F3 cell line were suspended in approximately 200 μL of RPMI medium containing 3.7 MBq of Chromium-51 (GE Healthcare Bio-Sciences), and then incubated in a 5% carbon dioxide gas incubator at 37° C. for one hour. After washing, the cell density was adjusted to 2×10⁵ cells/mL, and then the cells were added to a 96-well U-bottomed plate at 50 μL/well. Then, 50 μL of an antibody solution was added to each well. The plate was left to stand at room temperature for 15 minutes, and then 100 μL of effector cells (described below) were added to each well. The plate was then left to stand in a 5% carbon dioxide gas incubator at 37° C. for four to six hours. Thereafter, 100 μL of the supernatant was collected from each well, and used for the radioactivity measurement on a gamma counter (1480 WIZARD 3″, Wallac). The specific chromium release rate was calculated according to the following equation:

Specific chromium release rate (%)=(A−C)×100/(B−C)

where A represents the radioactivity (cpm) in each well, B represents the mean value of the radioactivity (cpm) in wells to which 50 μL of the cells and 150 μL of 2% Nonidet P-40 solution (Code No. 252-23, Nacalai Tesque) were added, and C represents the mean value of the radioactivity (cpm) in wells to which 50 μL of the cells and 150 μL of RPMI medium were added. The assay was conducted in duplicates, and the mean value and standard deviation were calculated for the specific chromium release rate. 3-3) Measurement of the ADCC Activity using Mouse spleen Cells as Effector Cells

Cells (SPL) prepared by adding 50 ng/mL of recombinant human interleukin-2 (Peprotech) to spleen cells prepared from C3H mice (Charles River Japan), or cells (SPL-LAK) prepared by culturing spleen cells in the presence of 50 ng/mL of recombinant human interleukin-2 for four days were used as the effector cells. The ADCC activity was measured according to 3-2). The number of effector cells per well was 5×10⁵ cells (SPL) or 2×10⁵ cells (SPL-LAK), and the ADCC induction time was six hours. Mouse IgG2a (Becton Dickinson) and human IgG1 (Serotec) were used as the negative control antibodies.

Low ADCC activity was detected for the DF366m antibody and low-fucose DF366m antibody, while hardly any ADCC activity was detected for the DF366c antibody and low-fucose DF366c antibody (FIG. 2).

3-4) Measurement of the ADCC Activity using FcγR-Expressing NK92 Cell Lines as Effector Cells

FcγR-expressing NK92 cell lines (Example 1, mouse FcγR4/human FcγR3-, mouse FcγR4/human γ-, mouse FcγR3/human FcγR3-, mouse FcγR3/human γ-, and human FcγR3-expressing NK92 cells) were used as the effector cells. The ADCC activity was measured according to 3-2). The number of effector cells per well was 5×10⁴ cells, and the ADCC induction time was four hours. Mouse IgG2a (Becton Dickinson) and human IgG1 (Serotec) were used as the negative control antibodies.

When mouse FcγR4/human FcγR3- and mouse FcγR4/human γ-expressing NK92 cells were used, the ADCC activity was detected for both the DF366m antibody and DF366c antibody, and the ADCC activity was more remarkably increased for the low-fucose DF366m antibody and low-fucose DF366c antibody (FIG. 3).

When mouse FcγR3/human γ-expressing NK92 cells were used, high ADCC activity was detected for the DF366m antibody, and the ADCC activity was further increased for the low-fucose DF366m antibody. Low ADCC activity was detected for the DF366c antibody and low-fucose DF366c antibody (FIG. 4).

The ADCC activity was low in mouse FcγR3/human FcγR3-expressing NK92 cells. This was speculated to be caused by low expression level of FcγR (FIG. 5).

When using human FcγR3 -expressing NK92 cells, high ADCC activity was detected for the DF366c antibody, and the ADCC activity was more remarkably increased for the low-fucose DF366c antibody. The DF366m antibody showed low ADCC activity, whereas high ADCC activity was detected for the low-fucose DF366m antibody (FIG. 6).

The above-mentioned results show that high ADCC activity can be detected when using chimeric FcγR-expressing NK92 cells, even if only low ADCC activity can be detected in mouse spleen cells. In particular, in mouse FcγR4-expressing NK92 cells, enhancement of the ADCC activity by the low-fucose antibodies was clearly demonstrated. In human FcγR3-expressing NK92 cells, the ADCC activity of the mouse antibodies could not be sufficiently detected. Thus, it was shown that chimeric FcγR-expressing NK92 cells are advantageous for measuring the ADCC activity of mouse antibodies.

Example 4 Measurement of the ADCC Activity of Anti-Claudin 3 Antibody

The ADCC activity of anti-claudin 3 monoclonal antibody was measured (FIG. 7). The MCF7 breast cancer cell line (purchased from ATCC) was used as target cells, and the measurements were performed as described in Example 3. The antibodies used were CDN16 (mouse IgG2b, H-chain amino acid sequence: SEQ ID NO: 55; L-chain amino acid sequence: SEQ ID NO: 56), CDN27 (mouse IgG2a, H-chain amino acid sequence: SEQ ID NO: 57, L-chain amino acid sequence: SEQ ID NO: 58), and CDN35 (mouse IgG2a, H-chain amino acid sequence: SEQ ID NO: 59, L-chain amino acid sequence: SEQ ID NO: 60). When SPL (4.5×10⁵ cells/well, and ADCC induction time of six hours) was used as the effector cells, hardly any ADCC activity could be detected. When mouse FcγR4/human FcγR3- and mouse FcγR4/human γ-expressing NK92 cells were used (5×10⁴ cells/well, and ADCC induction time of four hours), significant ADCC activity was detected. Amongthem, CDN35 showed high ADCC activity.

The above-mentioned results show that the use of chimeric FcγR-expressing NK92 cells enables detection of the ADCC activity, and allows accurate comparison of the ADCC activity of each antibody, even if the ADCC activity could not be detected sufficiently in mouse spleen cells.

INDUSTRIAL APPLICABILITY

Expression of chimeric proteins of the present invention in effector cells greatly reduces the labor for preparing effector cells for measuring the ADCC activity of mouse antibodies, and enables accurate measurements with small lot-to-lot differences. By utilizing effector cells expressing the chimeric proteins of the present invention, antibodies having cytotoxic activity, which are used for the treatment or prevention of diseases such as cancers or autoimmune diseases, can be efficiently screened. 

1. A chimeric protein comprising a mouse Fcγ receptor extracellular domain and a human γ chain transmembrane domain.
 2. The chimeric protein of claim 1, wherein the chimeric protein further comprises a human γ chain intracellular domain.
 3. A chimeric protein comprising a mouse Fcγ receptor extracellular domain and a human Fcγ receptor transmembrane domain.
 4. The chimeric protein of claim 3, wherein the chimeric protein further comprises a human Fcγ receptor intracellular domain.
 5. The chimeric protein of claim 3, wherein the human Fcγ receptor is human Fcγ receptor
 3. 6. The chimeric protein of claim 1, wherein the mouse Fcγ receptor is mouse Fcγ receptor
 3. 7. The chimeric protein of claim 1, wherein the mouse Fcγ receptor is mouse Fcγ receptor
 4. 8. A gene encoding the chimeric protein of claim
 1. 9. A vector comprising the gene of claim
 8. 10. A cell expressing the chimeric protein of claim
 1. 11. The cell of claim 10, wherein the cell is a human-derived cell.
 12. The cell of claim 10, wherein the cell is an NK cell.
 13. A method for measuring the cytotoxic activity of an antibody, wherein the method: (a) contacting a test antibody with a cell expressing an antigen to which the test antibody binds; (b) contacting the test antibody of (a) with the cell of claim 10; and (c) measuring the cytotoxic activity of the test antibody.
 14. The measurement method of claim 13, wherein the test antibody is a mouse-derived antibody.
 15. A method of screening for an antibody having cytotoxic activity, wherein the method comprises: (a) contacting a test antibody with a cell expressing an antigen to which the test antibody binds; (b) contacting the test antibody of (a) with the cell of claim 10; (c) measuring the cytotoxic activity of the test antibody; and (d) selecting an antibody having cytotoxic activity.
 16. The screening method of claim 15, wherein the test antibody is a mouse-derived antibody. 17-20. (canceled)
 21. The chimeric protein of claim 4, wherein the human Fcγ receptor is human Fcγ receptor
 3. 22. The chimeric protein of claim 3, wherein the mouse Fcγ receptor is mouse Fcγ receptor
 3. 23. The chimeric protein of claim 3, wherein the mouse Fcγ receptor is mouse Fcγ receptor
 4. 24. A gene encoding the chimeric protein of claim
 3. 25. A vector comprising the gene of claim
 24. 26. A cell expressing the chimeric protein of claim
 3. 27. The cell of claim 26, wherein the cell is a human-derived cell.
 28. The cell of claim 26, wherein the cell is an NK cell.
 29. A method for measuring the cytotoxic activity of an antibody, wherein the method comprises: (a) contacting a test antibody with a cell expressing an antigen to which the test antibody binds; (b) contacting the test antibody of (a) with the cell of claim 26; and (c) measuring the cytotoxic activity of the test antibody.
 30. The measurement method of claim 29, wherein the test antibody is a mouse-derived antibody.
 31. A method of screening for an antibody having cytotoxic activity, wherein the method comprises: (a) contacting a test antibody with a cell expressing an antigen to which the test antibody binds; (b) contacting the test antibody of (a) with the cell of claim 26; (c) measuring the cytotoxic activity of the test antibody; and (d) selecting an antibody having cytotoxic activity.
 32. The screening method of claim 31, wherein the test antibody is a mouse-derived antibody. 